Sandmeyer reactions, copper® bromide

Replacement of the Diazonium Group by Chloride, Bromide, and Cyanide The Sandmeyer Reaction Copper salts (cuprous salts) have a special affinity for diazonium salts. Cuprous chloride, cuprous bromide, and cuprous cyanide react with arenediazonium salts to give aryl chlorides, aryl bromides, and aryl cyanides. The use of cuprous salts to replace arenediazonium groups is called the Sandmeyer reaction. The Sandmeyer reaction (using cuprous cyanide) is also an excellent method for attaching another carbon substituent to an aromatic ring. 

Aryl chlorides and bromides are prepared by reaction of an arenediazonium salt with the corresponding copper(I) halide, CuX, a process called the Sandmeyer reaction. Aryl iodides can be prepared by direct reaction with Nal without using a copper(T) salt. Yields generally fall between 60 and 80%. 

When aqueous solutions of aromatic and heteroaromatic diazonium salts are treated with cuprous chloride, -bromide, or -cyanide, the corresponding aromatic chlorides, bromides, or cyanides are formed, respectively. In many cases the anions mentioned must be present in excess. This reaction, the Sandmeyer reaction, was discovered by Sandmeyer in 1884. A variant carried out with copper powder and HBr or HC1 was for many years called the Gattermann reaction (Gattermann, 1890). As it is often confused with the Gattermann-Koch reaction (ArH + CO + HC1 ArCHO), and as it is mechanistically not significantly different from Sandmeyer s procedure, the name Gattermann reaction should be avoided. 

Treatment of diazonium salts with cuprous chloride or bromide leads to aryl chlorides or bromides, respectively. In either case the reaction is called the Sandmeyer reaction The reaction can also be carried out with copper and HBr or HCl, in which case it is called the Gatterman reaction (not to be confused with 11-16). The Sandmeyer reaction is not useful for the preparation of fluorides or iodides, but for bromides and chlorides it is of wide scope and is probably the best way of introducing bromine or chlorine into an aromatic ring. The yields are usually high. 

Unsymmetrical 3,4-dihalo-l,2,5-thiadiazoles 118 and 119 were prepared from 3-amino-4-chloro-l,2,5-thiadiazole 117 via a Sandmeyer-like reaction involving successively tert-butyl nitrite and either copper bromide or copper iodide in anhydrous acetonitrile (Scheme 17) <2003H(60)29>. The bromo and iodo thiadiazoles 118 and 119 undergo selective Stille and Suzuki C-C coupling chemistry (see Section 5.09.7.6). 

One of the drawbacks of the Sandmeyer reaction is the number of competing side reactions leading to the formation of biaryls, azo compounds and phenols. A recent procedure to maximise the yield of aryl halide involves treatment of the arylamine with t-butyl nitrite and anhydrous copper(n) halide (the chloride or the bromide) in acetonitrile at 65 °C.28 The method is illustrated by the preparation of p-chloronitrobenzene (Expt 6.73) the overall reaction may be represented as ... 

A second method for preparing aryl halides is the Sandmeyer reaction. During a Sandmeyer reaction, a diazonium salt reacts with copper (I) bromide, copper (I) chloride, or potassium iodide to form the respective aryl halide. The diazonium salt is prepared from aniline by reaction with nitrous acid at cold temperatures. 

For the preparation of chlorides or bromides, the diazonium salt is decomposed with a solution of cuprous chloride or bromide in the corresponding halogen acid (Sandmeyer reaction). It is possible to prepare the aryl bromide from the diazonium chloride or sulfate. A variation Involves the use of copper powder and a mineral acid for the decomposition step (Gattermann reaction). Both procedures are illustrated by the syntheses of the isomeric bromotoluenes and chlorotoluenes. The usual conditions of the Sandmeyer reaction fail in the preparation of the chloro- and bromo-phenanthrenes. However, these compounds can be successfully obtained by the interaction of the diazonium compound with mercuric and potassium halides (Schwechten procedure). Another procedure for formation of aryl bromides involves treatment of the amine hydrobromide with nitrogen trioxide in the presence of excess 40% hydro-bromic acid. The Intermediate diazonium perbromide is then decomposed by heat. ... 

A diazonium salt reacts with copper(I) chloride or copper(I) bromide to form an aryl chloride or aryl bromide, respectively. This is called the Sandmeyer reaction. It provides an alternative to direct chlorination and bromination of an aromatic ring using CI2 or Br2 and a Lewis acid catalyst. 

Treatment of diazonium salts with cuprous, Cu(I), salts generates aryl halides. When 398 reacts with CuCl (cuprous chloride) or CuBr (cuprous bromide), the products are chlorobenzene or bromobenzene via what is probably a radical reaction.29l jhis conversion is known as the Sandmeyer reaction. 2 The use of copper powder rather than cuprous salts for this transformation is often called the Gattermann reaction. 93,292b,c Aryl iodides are also produced from diazonium salts by reaction with potassium iodide (KI) but the actual reactive species may be l3-.294,295 Treatment of aniline derivative 403 with sodium nitrite and HCl followed by treatment with KI, for example, gave a 89% yield of 404.Aryl nitriles are generated under Sandmeyer conditions using cuprous cyanide (CuCN), as in the conversion of 405 to benzonitrile derivative 407 via diazonium chloride, 406. 

Preparation of aryl bromides The Sandmeyer reaction using copper(l) bromide converts primary arylamines to aryl bromides. 

Aryl bromides and iodides are usually prepared from diazonium salts by a copper-catalyzed process, a reaction commonly known as the Sandmeyer reaction. Under the classic conditions of the Sandmeyer reaction, the diazonium salt is added to a hot acidic solution of the cuprous halide.It is also possible to convert anilines to aryl halides by generating the diazonium ion in situ. Reaction of anilines with alkyl nitrites and cuprous halides in acetonitrile gives good yields of aryl bromides by a copper-mediated process which is mechanistically similar to that occurring under the usual Sandmeyer conditions. Diazonium salts can also be converted to... 

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